Sterilization is the destruction of any virus, bacteria, fungus or other micro-organism, whether in a vegetative or in a dormant spore state and is defined by a 10−6 reduction in the level of bacteria. Conventional sterile processing procedures for medical instruments involve high temperature (such as steam and dry heat units) or chemicals (such as ethylene oxide gas, hydrogen peroxide, or ozone).
Sterilization methods and apparatus using gaseous sterilants are well known. Sterilizers using hydrogen peroxide as the sterilant are widely used. The hydrogen peroxide is generally supplied as an aqueous solution and evaporated prior to injection into a sterilization chamber of the sterilizer, by heating of the solution, or by applying a vacuum to the sterilization chamber, or both. After evaporation of the solution, the sterilization atmosphere in the sterilization chamber includes water vapor and hydrogen peroxide gas. It is a disadvantage of this process that the water vapor tends to condensate on articles in the chamber as the sterilization proceeds. The resulting layer of water condensate on the articles to be sterilized interferes with the sterilizing action of the hydrogen peroxide. Numerous apparatus and process modifications have been developed to address this problem, all of which are aimed at limiting the relative humidity in the sterilization atmosphere during the sterilization process. However, these modifications invariably increase operating cost and/or sterilization cycle times.
Sterilization processes using both hydrogen peroxide gas and ozone gas have been used, but with unsatisfactory results especially with respect to the sterilization of articles with long internal lumens, such as gastroscopes and colonoscopes, and with respect to cycle times and sterilization cost. Although ozone based processes are satisfactory with respect to sterilization of articles with long lumens, material compatibility represents a problem. Hydrogen peroxide based processes are generally unsatisfactory regarding the sterilization of long lumens. Undesired condensation of the hydrogen peroxide on the article to be sterilized reduces the sterilization efficiency. A reliable control of the hydrogen peroxide concentration in the sterilization chamber is important. Expensive systems are generally used to measure the concentration of hydrogen peroxide in the chamber.
Therefore, a method and apparatus is desired which would address at least one of the disadvantages of known sterilization processes using gaseous sterilants.